Someday, hopefully, science will figure out a cure for bad moods that doesn't involve eating an entire chocolate cake. (That's my method, and I've got the spare tire to prove it.)
Until then, I've found a Web site that's pretty good at soothing the savage beast. It's called MoodTurn, and it plays relaxing, New Age-y music mixed with the sounds of nature--at the same time treating you to a peaceful nature scene. In no time at all, you'll be down from the clock tower and surrendering your rifle to the authorities.
The site's controls might seem a tad confusing at first. Start by clicking the Player menu up top, then click Select Your Theme to choose between 10 lovely soundscapes: Birds, Beach, Bonfire, Storm, and and so on. You can also click Background and choose from lovely landscapes that match your selected theme.
But these steps are optional: MoodTurn will automatically cycle the images and music without any input from you.
Even if you're not stressed out, MoodTurn's music can serve as wonderful white noise while you work. The service is free, and there's nothing to install: it works inside your browser. I find myself using it more and more during my workday. (Not that I'm all that stressed, mind you, but I really enjoy the rain falling, birds chirping, etc.)